The subject invention relates to the art of wire feeding mechanisms and more particularly to drive rollers in wire feeding mechanisms that are used to driveably advance welding wire.
Wire feeding mechanisms have been provided heretofore, and generally, as shown in Seufer for example, have a wire pathway through which a continuous length of wire is advanced. Positioned on opposing sides of the wire pathway is at least one steel drive roller. Each steel drive roller is mounted on a roller support, and all of the roller supports are driveably engaged with one another. Accordingly, all of the steel drive rollers rotate in response to the movement of the corresponding roller support and thereby act to driveably advance the continuous length of wire. In order to impart an advancing force and motion to the wire, the opposing steel drive rollers are positioned sufficiently close to, one another so that the wire extending along the pathway is compressed between the opposing rollers. The compressive force in combination with the coefficient of friction, between the material of the wire and the steel roller, produces a frictional force along the wire which is greater than the force required to advance the continuous length of wire. As a result, the wire is advanced in a generally smooth and continuous motion in response to the rotation of the steel drive rollers.
Wire feeding mechanisms of the foregoing nature are utilized in a variety of applications. In many such applications, including welding operations, the advancing wire is subjected to a variety of non-uniform radial and axial impact loads. These loads normally react back through the wire to the feeding mechanism, at which point one of three results will normally occur. One result may be that the impact load will be absorbed by the system creating a minimal amount of slippage between the drive rollers and the wire causing only a brief change in wire feed speed (WFS). It will be appreciated that a consistent wire feed speed is critical to a high quality welding operation, and that anything more than a momentary deviation from the set WFS will result in low quality or failed welding operations. A second result is that the impact force reacting back to the feeding mechanism through the wire will exceed the frictional force between the steel drive rollers and the wire, and cause the drive rollers to slide against the surface of the wire causing the wire to become galled and deformed, and resulting in an extended deviation of the WFS from that desired. As previously indicated this may cause a significant reduction in the quality of the welding operation. What""s more, this causes additional impact loads to be created as the galled and deformed section of wire travels along the wire pathway. These additional impact loads react back to the wire feeding mechanism potentially initiating the cycle over and over again. Furthermore, the galled and deformed wire section will not melt uniformly during the welding operation resulting in inconsistent and lower quality welds. A third result is that the impact force will not exceed the frictional force between the drive rollers and the wire, but will exceed the column strength of the wire causing the wire to bend out of the pathway and become caught inside the wire feeding mechanism, resulting in a xe2x80x9cbird nestxe2x80x9d inside the wire feeder. Once the wire is bent out of the wire pathway the wire cannot be advanced along the pathway. Likewise, the wire being fed behind the bent wire portion cannot advance along the pathway and therefore becomes bent itself. In just a few seconds, a large number of bent wire segments have piled up adjacent the wire feeding device. At this point, production must be stopped and the wire feeding mechanism disassembled so that the xe2x80x9cbird nestxe2x80x9d can be cut out. The wire feeder can then be reassembled and production resumed. This creates a significant loss in production time, wire and other materials.
As can be appreciated from the foregoing discussion, a wire feeding mechanism can be made to function quite well if the wire being fed has a high column strength value. In such case, the compression force from the steel drive rollers can be set very high, creating a high friction force which resists sliding of the wire against the drive rollers in reaction to impact loads. Since the wire will not slide against the steel drive rollers, the impact loads will act as a column load on the advancing wire. However, if the column strength of the wire is high, then the wire will not be bent by the column load and the wire will continue to be fed to the downstream welding operation.
It will be further appreciated that the column strength of a length of round wire is dependent upon the diameter of the wire, and the material from which the wire is made. Steel wire can be made to work well in wire feeding mechanisms of the foregoing description. However, many nonferrous metals, such as aluminum, for example, are soft and do not possess sufficient column strength to permit problem-free operation of a wire feeding mechanism. As a result, if the compressive force from the steel drive rollers is low enough to avoid exceeding the column strength of the wire as impact loads react back to the wire feeding mechanism, then the resulting frictional force will be low enough to allow the wire to slide against the steel drive rollers and become galled and deformed. Furthermore, if the compressive force from the steel drive rollers is high enough to prevent sliding, the impact loads will often exceed the column strength of the nonferrous wire and cause a xe2x80x9cbird nest.xe2x80x9d Additionally, the steel drive rollers of the wire feeding mechanism tend to deform the relatively soft nonferrous wires regardless of the value of the compressive forces used. This further increases the likelihood of impact loads, and also reduces the consistency of the melt of the wire causing low quality welding of nonferrous metals. It will be appreciated for the foregoing reasons that the compressive forces cannot simply be reduced to minimize the deformation. As a result, traditional wire feeding mechanisms cannot provide the desired trouble-free operation when feeding nonferrous wires.
In accordance with the present invention, a drive roller is provided for a wire feeding mechanism which enables avoiding or minimizing the problems and difficulties encountered with the use of feed devices of the foregoing character, while promoting and maintaining the desired trouble-free operation, simplicity of structure, and economy of manufacture thereof. More particularly in this respect, a drive roller in accordance with the present invention includes a hub and a flexible outer cover, and a wire feeding mechanism incorporating drive rollers according to the present invention includes a wire pathway along which a continuous length of wire extends, and at least two drive rollers mounted on opposite sides of the wire pathway, each having a hub and a flexible outer cover. The drive rollers on one side of the wire pathway are radially adjustable relative to the opposing drive rollers. By changing the radial position of the adjustable drive rollers, the compressive force of the drive rollers on the wire extending therebetween is increased or decreased. With nonferrous wire, the traditional steel drive rollers of existing wire feeding mechanisms would increasingly deform the wire as the compression force was increased. The flexible covers of the drive rollers of the subject invention, however, deform as the compression force between the drive rollers is increased while the nonferrous wire does not. As a result, without damaging or deforming the nonferrous wire, significantly higher compressive forces can be maintained between the subject drive rollers and nonferrous wire than could be maintained between traditional steel drive rollers and nonferrous wire. This results in the ability to create a higher frictional force between the drive rollers and the wire, and this in turn provides increased ability to withstand impact loads without the wire sliding relative to the rollers.
Furthermore, the flexible covering of the drive rollers in the subject invention increasingly conforms to the arcuate surface contour of the wire as the drive rollers are brought closer to the wire pathway, whereby the compressive force is progressively increased on the wire. This acts to provide additional support and stability to the wire as it exits the drive rollers at the point which buckling of the wire due to low column strength begins to become an issue. It is well known that column strength is most directly related to the unsupported length and radius of a cylindrical column. However, the end conditions of the column are also important. As can be appreciated, a drive roller that provides a greater degree of radial support by conforming to the outside surface of the wire will provide a more rigid and more stable end condition. As such, the flexible covering of the drive rollers in the subject invention is able to provide an improved end condition, and therefore increased column strength over traditional steel drive rollers. The foregoing discussion is centered around nonferrous wire, for which column strength is a more significant issue. However, the drive rollers of the subject invention are suitable for use on ferrous and other types of wire as well, and provide the same benefits as discussed above, and hereinafter.
Finally, it is well known that the coefficient of friction is due to the interengagement of surface imperfections between two adjacent surfaces. The traditional steel drive rollers generally have relatively smooth surfaces contacting the wire so that the wire is not damaged by the contact of the drive roller. However, such a smooth surface has a relatively low coefficient of friction leading to a lower frictional force resulting between the wire and the drive rollers. The only way to increase the frictional force without increasing the compression force of the drive rollers is to increase the coefficient of friction between the drive rollers and the wire. This can be best accomplished by reducing the surface finish of the drive roller to make the surface contacting the wire rougher. However, as previously indicated, a rough finish on the traditional steel drive rollers will damage the wire and contribute to undesirable impact loads. However, with the drive rollers of the subject invention the surface finish can be made as rough or as smooth as is necessary to increase or decrease the coefficient of friction as desired without causing any damage to the wire. Additionally, the material of the flexible cover of the drive rollers in the subject invention may be selected from a wide variety of materials, including both plastics and rubbers. These materials can be compounded with a wide variety of additives to further increase or reduce the coefficient of friction and improve operation of the wire feeding mechanism.
It is accordingly an outstanding object of the present invention to provide a drive roller for a wire feeding mechanism having a flexible outer surface that is adapted to driveably advance a continuous length of welding wire in a consistent and effective manner without deforming or otherwise damaging the wire as it advances through the wire feeding mechanism.
Another object is the provision of a drive roller of the foregoing character in which the outer surfaces of opposed drive rollers conform to the wire as the wire extends therebetween, and thereby more fully provides radial support of the wire to improve the column strength thereof.
Still another object is the provision of a drive roller of the foregoing character in which the wire contacting surface of the drive roller can be formed from any one of a variety of different materials, such as plastic or rubber, and can have a variety of different surface finishes or conditions to increase or decrease the coefficient of friction with the wire being advanced.
A further object is the provision of a drive roller of the foregoing character which is easily maintained, and is comprised of a minimal number of parts and is structurally simple, thereby promoting the economic production of the drive rollers.
Yet a further object is the provision of a wire feeding mechanism incorporating drive rollers of the foregoing character, whereby a continuous length of welding wire can be advanced through the feeding mechanism in a consistent and effective manner without determining or otherwise damaging the wire.